Immunization of chickens with Salmonella enterica subspecies enterica serovar Enteritidis pathogenicity island-2 proteins

Several structural components of the type III secretion systems (T3SS) encoded by Salmonella pathogenicity island (SPI)-1 and SPI-2 are exposed to the host's immune system prior to/during the infection/invasion process, making them potential vaccine candidates. In this study we evaluated whether chickens vaccinated with SPI-2 T3SS components could mount a significant humoral immune response (as measured by serum IgG titres) and whether these antibodies could be transferred to progeny (as measured by egg yolk IgG titres), and whether vaccinates and progeny of vaccinates could be protected against challenge with SE. The results of our studies show that vaccinated chickens do produce high levels of SPI-2 T3SS specific serum IgG that they are able to transfer to their progeny. It was demonstrated that vaccinates and progeny of vaccinates had lower overall countable recovered Salmonella enterica subspecies enterica serovar Enteritidis (SE) per bird in most situations.     

Detection of specific antibodies against deflagellated Salmonella Enteritidis and S. Enteritidis FliC-specific 9kDa polypeptide

Specific antibody levels of laying hens and young chickens experimentally infected with Salmonella Enteritidis and vaccinated farm flocks were evaluated by enzyme-linked immunosorbent assays (ELISAs) with two different antigens, deflagellated S. Enteritidis whole cell (DEWC) and S. Enteritidis FliC-specific 9kDa polypeptide (SEP9). Infected laying hens excreted S. Enteritidis throughout the experimental period, and the specific antibody titers in DEWC-ELISA, were significantly higher than the uninfected group. It suggests that this DEWC-specific antibody will serve as an effective indicator of S. Enteritidis infection, especially for non-vaccinated laying flocks. SEP9-specific antibodies were detected in spray-inoculated young chickens but not in oral-inoculated young chickens. Compared with greatly high SEP9-specific antibody levels of vaccinated farm flocks, no response was observed in orally infected hens. These results indicate that S. Enteritidis discontinues expressing SEP9 once it has crossed the intestinal barrier, and that SEP9-ELISA will serve as a valuable monitoring tool for the status of S. Enteritidis vaccination on a flockwide basis, independent of stable S. Enteritidis infections.     

Protection conferred by a live Salmonella Enteritidis vaccine against fowl typhoid in laying hens

Fowl typhoid is under control in poultry farms of developed countries, but it still endemically subsists in commercial laying hen farms of some countries. It has been demonstrated that Salmonella live vaccines can elicit cross-immunity against members of the same Kauffmann-White scheme serogroup. In this work, we explored the protection conferred by TAD Salmonella vac E, a live Salmonella enterica serovar Enteritidis vaccine, against fowl typhoid. Three groups of laying hens were vaccinated with different vaccination schedules starting on the first day of life, and afterwards were infected with 2 x 10(5) CFU of a virulent Salmonella Gallinarum strain, either at wk 28 or wk 52. Mortality, fecal shedding, and organ invasion of Salmonella Gallinarum were assessed. In this work we demonstrated that this Salmonella Enteritidis vaccine is able to cross-immunize against Salmonella Gallinarum. At wk 28, hens vaccinated with three oral doses or with two oral doses combined with one subcutaneous dose were protected by the vaccine. At wk 52, when hens were infected 36 wk after the final immunization, the vaccine was not able to confer protection. Thus, revaccination every 3 mo would be highly recommended. In countries where Salmonella Gallinarum subsists together with Salmonella Enteritidis, control programs should include vaccination of laying hens using safe attenuated Salmonella strains.     

Early immune dynamics following infection with Salmonella enterica serovars Enteritidis, Infantis, Pullorum and Gallinarum: cytokine and chemokine gene expression profile and cellular changes of chicken cecal tonsils

Salmonella enterica subspecies enterica infection remains a serious problem in a wide range of animals and in man. Poultry-derived food is the main source of human infection with the non-host-adapted serovars while fowl typhoid and pullorum disease are important diseases of poultry. We have assessed cecal colonization and immune responses of newly hatched and older chickens to Salmonella serotypes Enteritidis, Infantis, Gallinarum and Pullorum. S. Enteritidis and S. Infantis colonized the ceca more efficiently than S. Gallinarum and S. Pullorum. Salmonella infection was also associated with increased staining for B-lymphocytes and macrophages in the cecal tonsils of infected birds. S. Enteritidis infection in newly hatched birds stimulated the expression of CXCLi1 and CXCLi2 chemokines in the cecal tonsils, while S. Gallinarum up-regulated the expression of LITAF. In older chickens, S. Enteritidis infection resulted in a significantly higher expression of CXCLi2, iNOS, LITAF and IL-10 while S. Pullorum appeared to down-regulate CXCLi1 expression in the cecal tonsils. Data from spleens showed either no expression or down-regulation of the tested genes.     

Effects of Salmonella enterica subsp. enterica serovar Enteritidis vaccination in layer hens subjected to S. Enteritidis challenge and various feed withdrawal regimens

Levels of Salmonella enterica subsp. enterica serovar Enteritidis infection and serum S. Enteritidis antibodies after experimental S. Enteritidis challenge and feed withdrawal were investigated in S. Enteritidis-vaccinated and unvaccinated hens. The results were used to determine whether formalin-inactivated S. Enteritidis vaccination can protect layer hens from S. Enteritidis challenge during feed withdrawal periods. S. Enteritidis infection rates were evaluated from cloacal swabs, eggs and organs. Serum antibody titers to deflagellated S. Enteritidis whole cells (DEWC) and S. Enteritidis FliC-specific 9-kDa polypeptide (SEp 9) were examined by commercial ELISA kits. Cloacal S. Enteritidis recovery rates were lower in the vaccinated than unvaccinated group. Recovery rates of S. Enteritidis from samples increased after feed withdrawal and decreased after re-introduction of feed. S. Enteritidis counts in cloacal swabs were lower in the vaccinated than in the unvaccinated group (P<0.05). More S. Enteritidis-positive eggs were detected from the unvaccinated group. Before S. Enteritidis challenge, the DEWC ELISA titer of the vaccinated group was higher (P<0.05) than the unvaccinated group; subsequently, the S. Enteritidis DEWC ELISA titers of both groups increased gradually. In contrast, only the vaccinated group elicited high SEp-9 antibody titer during post-challenge and feed withdrawal. Additionally, vaccinated hens yielded negative S. Enteritidis isolation rates from egg contents. There is a correlation between negative S. Enteritidis isolation rates and high SEp 9 titers in vaccinated layer hens challenged with S. Enteritidis and subjected to feed withdrawal regimens. These findings suggest the S. Enteritidis vaccination of pullets may protect against S. Enteritidis infection during forced molting and that SEp 9 titer could be a potential indicator of antibody protection against S. Enteritidis infection. The potential of the SEp 9 peptide as an antigen for S. Enteritidis vaccination in the future is worth noting.     

SPI-1-encoded type III secretion system of Salmonella enterica is required for the suppression of porcine alveolar macrophage cytokine expression

ABSTRACT: Genes localized at Salmonella pathogenicity island-1 (SPI-1) are involved in Salmonella enterica invasion of host non-professional phagocytes. Interestingly, in macrophages, SPI-1-encoded proteins, in addition to invasion, induce cell death via activation of caspase-1 which also cleaves proIL-1β and proIL-18, precursors of 2 proinflammatory cytokines. In this study we were therefore interested in whether SPI-1-encoded type III secretion system (T3SS) may influence proinflammatory response of macrophages. To test this hypothesis, we infected primary porcine alveolar macrophages with wild-type S. Typhimurium and S. Enteritidis and their isogenic SPI-1 deletion mutants. ΔSPI1 mutants of both serovars invaded approx. 5 times less efficiently than the wild-type strains and despite this, macrophages responded to the infection with ΔSPI1 mutants by increased expression of proinflammatory cytokines IL-1β, IL-8, TNFα, IL-23α and GM-CSF. Identical macrophage responses to that induced by the ΔSPI1 mutants were also observed to the infection with sipB but not the sipA mutant. The hilA mutant exhibited an intermediate phenotype between the ΔSPI1 mutant and the wild-type S. Enteritidis. Our results showed that the SPI-1-encoded T3SS is required not only for cell invasion but in macrophages also for the suppression of early proinflammatory cytokine expression.     

The Salmonella Pathogenicity Island 2 regulator ssrA promotes reproductive tract but not intestinal colonization in chickens

Using a deletion mutant in the regulator of SPI-2, ssrA, we investigated the role of SPI-2 in invasion, intestinal colonization and reproductive tract infection of chickens by Salmonella Enteritidis. The ssrA mutant was fully invasive in phagocytic and non-phagocytic cells but failed to persist within chicken macrophages. The ability of Salmonella Enteritidis to cause disease in orally infected 1-day-old chicks was not altered when ssrA was deleted. Furthermore, caecal colonization was not affected, while spleen and liver showed reduced colonization. Following intra-peritoneal and intravenous infection of 1-day-old chicks, internal organ colonization was strongly reduced. After intravenous inoculation in adult laying hens bacterial numbers of the ssrA mutant were significantly lower in oviducts and ovaries as compared to the wild type strain. The chickens showed less reproductive tract lesions and the recovery of egg production were faster compared to the wild type strain infected chickens. These findings indicate that the SPI-2 regulator ssrA promotes reproductive tract colonization, but is not essential for intestinal colonization of chickens with the host non-specific serotype Enteritidis.     

植物乳酸杆菌对感染肠炎沙门氏菌蛋鸡生产性能、蛋品质及血浆生化指标的影响

为研究植物乳酸杆菌对感染肠炎沙门氏菌蛋鸡生产性能、蛋品质及血浆生化指标的影响,本试验选用400只沙门氏菌阴性蛋鸡,随机分成4个处理组,每处理组5个重复,每个重复20只试鸡。试验第1周,对照组（T1、T3组）饲喂基础日粮,试验组（T2、T4组）在基础日粮添加2×10⁸ CFU/g植物乳酸杆菌。饲喂1周后,T3、T4组试鸡连续2 d灌服1 mL肠炎沙门氏菌悬浮液（1.0×10⁸ CFU/mL）,T1、T2组试验鸡口服等量无菌PBS溶液。结果显示：①蛋鸡感染肠炎沙门氏菌后可极显著降低产蛋率（P_SE=0.02）及平均日采食量（P_SE=0.01）。添加植物乳酸杆菌可显著提高产蛋率（P_LP=0.02）,显著降低料蛋比（P_LP=0.04）。②蛋鸡感染肠炎沙门氏菌后,添加植物乳酸杆菌可显著增加蛋壳厚度（P_LP=0.01）和蛋壳强度（P_LP=0.02）,显著降低蛋黄颜色（P_LP=0.02）。③蛋鸡感染肠炎沙门氏菌后可极显著提高蛋鸡血浆中碱性磷酸酶（ALP）含量（P_SE<0.01）,植物乳酸杆菌干预可显著提高谷草转氨酶（AST）（P_LP=0.02）、钙（P_LP=0.04）和磷（P_LP=0.04）的含量。综上所述,植物乳酸杆菌可显著改善蛋鸡生产性能和蛋品质,维持蛋鸡生理生化指标稳定,同时可缓解沙门氏菌带来的病理损伤,保障蛋鸡机体健康。     

Salmonella enterica serovar Typhimurium and Enteritidis infection of pigs and cytokine signalling in palatine tonsils

Pigs are considered as one of the major sources of zoonotic strains of Salmonella enterica for humans. Out of many S. enterica serovars, S. Typhimurium dominates in pigs, however, in several countries in Central Europe, S. Enteritidis is also quite frequent in pig herds. In this study we therefore compared the colonisation of pigs with S. Typhimurium and S. Enteritidis. We found that 3 weeks after infection S. Enteritidis 147 colonised the intestinal tract in higher quantities but was shed in faeces in lower quantities than S. Typhimurium 17C10. In a second experiment we found out that S. Enteritidis 147 and its SPI-1 and SPI-4 mutants increased proinflammatory cytokine (IL-1β and IL-8) signalling in the ileum 5 days post infection. On the other hand, independent of SPI-1 or SPI-4, S. Enteritidis 147 suppressed expression of IL-18, MCP1, TLR2, CD86, IL-7, IL-10 and IL-15 in the palatine tonsils. The suppression of cytokine signalling may facilitate the initial colonisation of the palatine tonsils by Salmonella. Moreover, immune suppression may also influence pig resistance to opportunistic pathogens and Salmonella infection in pigs thus may become an issue not only in terms of pork contamination but also in terms of affecting the immunological status of pig herds.     

An attenuated Salmonella Enteritidis strain derivative of the main genotype circulating in Uruguay is an effective vaccine for chickens

We have recently reported that Salmonella enterica serovar Enteritidis (S. Enteritidis) strains circulating in Uruguay, are unevenly distributed among different genetic subtypes, with a predominant genotype that is a common contaminant of poultry-derived food and that accounts for the vast majority of human cases of food-borne disease. Herein, we describe the construction of a genetically-defined aroC derivative (LVR02) of a local strain of S. Enteritidis belonging to the major genetic type. We demonstrated the attenuation and the immunogenicity of that strain in a mouse model, and evaluated it as a vaccine for commercial layer chickens. LVR02 proved to be stable, attenuated, innocuous, immunogenic and to induce protective immunity against a S. Enteritidis challenge when used for oral vaccination. A single oral dose of LVR02 administered to newly hatched chickens induced protection against oral challenge with the parental virulent strain, preventing systemic and persistent intestinal infection and significantly reducing the shedding of the challenge strain in birds' feces. A second vaccine dose at 15 days post-hatching boosted the immunogenicity of the vaccine, and strengthened the protection achieved with a single dose. This strain may represent the basis of a live vaccine to be included in national control programs to reduce circulation of this pathogen in the country.     

Efficacy of soluble recombinant FliC protein from Salmonella enterica serovar enteritidis as a potential vaccine candidate against homologous challenge in chickens

FliC, the flagellin antigen of Salmonella Enteritidis, was tested as a vaccine candidate for protective effect against a homologous challenge in chickens. After immunization with recombinant FliC (rFliC) or administration of phosphate-buffered saline (PBS) at 56 days old, the chickens were challenged with 10(9) colony-forming units of Salmonella Enteritidis at 76 days old. The vaccinated birds showed significantly decreased bacterial counts in the liver and cecal contents compared to those administered PBS at 7 days postchallenge, but the protection was partial. The replication experiment also showed a similar result. In both experiments, vaccination induced an increased level of serum anti-rFliC IgG, which was also reactive to the native flagella. The intestinal IgA level was slightly higher in the vaccinated birds than in the control. However, neither the proliferative response nor interferon-gamma secretion of splenic cells upon stimulation with rFliC was induced. Therefore, the effect of rFliC as a vaccine is limited, and further improvement is needed.     

Preliminary evaluation of the use of the sefA fimbrial gene to elicit immune response against Salmonella enterica serotype Enteritidis in chickens

In the last 2 decades, the prevalence of Salmonella enterica serotype Enteritidis (Salmonella Enteritidis) has dramatically increased worldwide, becoming the leading cause of food-borne illnesses and an important public health issue. Many studies have suggested the role of the SEF14 fimbrial protein in the adhesion of Salmonella Enteritidis to the host. In the present study, the sefA gene, which encodes the main subunit of the SEF14 fimbrial protein, was cloned into a temperature-sensitive expression vector and transformed into a nonpathogenic, avirulent strain of Escherichia coli. The recombinant strain was used as a vaccine to elicit specific immune response against the SefA protein of Salmonella Enteritidis in 1-day-old chickens. The recombinant strain was reisolated from the intestines of treated birds for up to 21 days posttreatment, demonstrating its ability to colonize the intestinal tracts of 1-day-old chickens. In addition, immunoglobulin A (IgA) against the SefA protein was detected in intestinal secretions from treated birds at 7 days posttreatment and in bile samples from 14 to 21 days posttreatment by enzyme-linked immunosorbent assay. Nontreated birds did not show any evidence of intestinal colonization by the recombinant strain or anti-SefA IgA response in their bile or intestinal secretions. Preliminary evaluation of the recombinant strain showed a potential use of this strain to elicit protection against Salmonella Enteritidis infection in chickens. Further experiments are needed to study the ability of the recombinant strain to protect birds against Salmonella Enteritidis colonization.     

Competitive exclusion by Bacillus subtilis spores of Salmonella enterica serotype Enteritidis and Clostridium perfringens in young chickens

Cost effective control of avian diseases and food borne pathogens remains a high priority for all sectors of the poultry industry with cleansing and disinfection, vaccination and competitive exclusion approaches being used widely. Previous studies showed that Bacillus subtilis PY79(hr) was an effective competitive exclusion agent for use in poultry to control avian pathogenic Escherichia coli serotype O78:K80. Here we report experiments that were undertaken to test the efficacy of B. subtilis PY79(hr) in the control of Salmonella enterica serotype Enteritidis and Clostridium perfringens in young chickens. To do this, 1-day-old and 20-day-old specific pathogen free (SPF) chicks were dosed with a suspension of B. subtilis spores prior to challenge with S. Enteritidis (S1400) and C. perfringens, respectively. For both challenge models, a single oral inoculum of 1x10(9) spores given 24h prior to challenge was sufficient to suppress colonisation and persistence of both S. Enteritidis and C. perfringens. In particular, the faecal shedding of S. Enteritidis, as measured by a semi-quantitative cloacal swabbing technique, was reduced significantly for the 36 days duration of the experiment. B. subtilis persisted in the intestine although with decreasing numbers over the same period. These data add further evidence that B. subtilis spores may be effective agents in the control of avian diseases and food borne pathogens.     

Protection of laying hens against Salmonella Enteritidis by immunization with type 1 fimbriae

Eighteen chickens were immunized subcutaneously with purified type 1 fimbriae from Salmonella enterica serotype Enteritidis at 18 and 21 weeks of age. Evidence of IgG and IgA responses was found in the eggs and in the sera of the immunized hens. Three weeks later, immunized and non-immunized chickens (n=18) were challenged intravenously with 2x10(7) live Salmonella enterica serotype Enteritidis. There was no significant difference in the numbers of eggs laid by immunized and non-immunized birds. The percentage of Salmonella contaminated eggs was significantly higher in the non-immunized group than in the immunized group due to a higher percentage of contamination of the externally disinfected egg shells. There were no statistical differences in the percentages of contaminated yolks and egg whites between control and immunized birds. No differences in the number of colonizing bacteria could be found in the spleen nor in the liver between the immunized and the control groups throughout the experiment. Salmonella was cleared from the ovary of the immunized birds in the second week p.i., in contrast to the control birds where Salmonella was isolated till the third week after infection. Oviducts were significantly more infected in the control group than in the immunized group. Salmonella was cleared from the oviducts at 3 weeks p.i. in the immunized hens but not in the control hens. In conclusion, we demonstrated that the immunization of laying hens with type 1 fimbriae reduced the number of contaminated eggs and reduced the colonization of the reproductive organs.     

Comparison of real-time PCR with conventional PCR and culture to assess the efficacy of a live attenuated Salmonella enterica serovar Typhimurium vaccine against Salmonella enterica serovar Enteritidis in commercial leghorn chicks vaccinated under field and laboratory conditions

The efficacy of a live attenuated Salmonella Typhimurium Megan Vac 1 vaccine (MV1) was evaluated against Salmonella Enteritidis in chicken pullets with the use of PCR and culture methods. Two hundred Hyline W-32 white leghorn chicks were obtained from a local hatchery and divided into four treatment groups. Two of the groups served as positive and negative controls. The MV1 vaccine was administered to the chicks in the remaining two groups at 1 and 35 days old by either the coarse spray (field) or the oral route (laboratory) method. The chicks were challenged with a high dose of a Salmonella Enteritidis strain at 10 wk old and euthanatized 3 days postinoculation. Samples for PCR analysis were collected prior to enrichment, after pre-enrichment in buffered peptone water (BPW) and after primary enrichment from the ceca, liver, and spleen. None of the samples tested yielded positive results for the Salmonella Typhimurium vaccine strain by either the culture or PCR methods. Results from the standard culture method showed that vaccinating the birds with MV1 reduced the counts of Salmonella Enteritidis recovered from the challenged birds. In addition, fewer pre-enriched samples tested positive for Salmonella Enteritidis among the challenged groups that were vaccinated when compared to the unvaccinated challenged group. Under the conditions of this study, MV1 was unable to prevent colonization of other internal organs such as the liver and spleen. Real-time PCR was significantly more sensitive than conventional PCR (C-PCR) prior to enrichment, but after enrichment the sensitivities of the two methods were similar. Enrichment significantly increased the sensitivity of both PCR methods for the detection of Salmonella Enteritidis in cecal samples, but did not significantly increase the sensitivity for detection of Salmonella Enteritidis in liver and spleen samples that were pre-enriched in BPW. There was no significant difference between the laboratory or field vaccination methods with respect to either the prevalence of Salmonella Enteritidis isolation or the bacterial loads in culture-positive samples. Collectively, the data suggest that MV1 offered some protection against Salmonella Enteritidis in commercial layer chick pullets under the conditions of this study. Given the labor and time required to perform the C-PCR and culture methods, the real-time PCR method may prove to be a more useful method to use in diagnostics.     

Passive protection against Salmonella enterica serovar Enteritidis infection from maternally derived antibodies of hens vaccinated with a ghost vaccine

This study evaluated maternal immunity against Salmonella enterica serovar Enteritidis acquired through the egg yolk. Two-hundred 19-week-old specific pathogen free (SPF) broiler breeders which were randomly divided into two groups of equal size were injected with S. Enteritidis ghosts (5 × 10⁹ colony forming units in 0.1 ml per hen) and phosphate-buffered saline (PBS, 0.01 mol⋅l⁻¹, pH 7.4) twice, respectively, with an interval of 2 weeks. An indirect enzyme-linked immunosorbent assay (ELISA) was applied to detect specific antibodies against S. Enteritidis. S. Enteritidis-specific antibody levels in the vaccinated group increased over time and were significantly higher than those of the control group on days 28 (P < 0.001) and 35 (P < 0.001) post-vaccination. Ten 7-day-old chicks from hens that were vaccinated with a S. Enteritidis ghost vaccine were challenged at 14 days of age with 5 × 10⁹ CFU of S. Enteritidis DH091 (homologous to the vaccine strain), 8/10 (80%) chicks from vaccinated hens survived, whereas 3/10 (30%) chicks from unvaccinated hens survived. The chicks acquired high levels of serum antibodies against S. Enteritidis. These results reveal that maternal antibodies in chicks acquired from vaccinated hens through eggs can confer a significant protection against S. Enteritidis infection.     

Exploitation of intestinal colonization-inhibition between salmonella organisms for live vaccines in poultry: potential and limitations

Immunization represents one of the most important methods to increase the resistance of chickens against Salmonella infection. In addition to the development of an adaptive immune response, oral administration of live Salmonella strains to day-old chicks provides protection against infection within hours by intestinal colonization-inhibition. For the exploitation of this phenomenon, practical information on colonization-inhibition between Salmonella organisms is needed. Colonization-inhibition capacity between Salmonella strains from serogroups B, C1, C2, D and G was assessed in chickens. The most profound level of intestinal colonization-inhibition occurred between isogenic strains. Inhibition between strains of the same serovar was greater than that between strains of different serovars. The degree of inhibition between different serovars was not sufficiently high to identify a single strain which might inhibit a wide range of other Salmonella organisms. However, as Salmonella Enteritidis is the dominant serovar in poultry in many countries and because of the profound colonization-inhibition within this serovar there is a considerable potential to exploit this phenomenon in the development of novel live S. Enteritidis vaccines. Treatment of young chicks with mixtures of different Salmonella serovars resulted not only in a very strong growth inhibition of the isogenic strains but also in a substantial inhibition of heterologous serovars. The potential of mixtures of heterologous Salmonella strains as a 'Salmonella Inhibition Culture' and as a 'live Salmonella vaccine' should be further explored.     

Humoral immune response in hens naturally infected with Salmonella Enteritidis against outer membrane proteins and other surface structural antigens

A simple procedure for obtaining surface exposed antigens of Salmonella Enteritidis is described. A heat treatment of whole bacteria in saline solution induced the release of small membrane vesicles containing outer membrane components as well as surface appendage components, such as fimbriae and flagellin. The characterization of the structural components of this extract, called HE, was established by SDS-PAGE and immunoblotting using polyclonal and monoclonal specific antibodies. Five major groups of proteins were identified: flagellin, porins, OmpA, SEF21 and SEF14 fimbriae. The immunogenicity of these proteins was studied by immunoblotting with serum samples from naturally infected hens. Flagellin, porins, OmpA, SEF14 and SEF21 fimbriae were immunogenic in the S. Enteritidis infected hens (frequency of reactants: 47.3, 97.3, 64.7, 50.0 and 60.8%, respectively); porins also reacted with sera from non infected hens (66.7%). The immunogenicity of these antigens in infected birds provide promise that they may serve as components of an effective subcellular vaccine for poultry salmonellosis.     

A comparison of transmission characteristics of Salmonella enterica serovar Enteritidis between pair-housed and group-housed laying hens

ABSTRACT: Human cases of bacterial gastro-enteritis are often caused by the consumption of eggs contaminated with Salmonella species, mainly Salmonella enterica serovar Enteriditis (Salmonella Enteritidis). To reduce human exposure, in several countries worldwide surveillance programmes are implemented to detect colonized layer flocks. The sampling schemes are based on the within-flock prevalence, and, as this changes over time, knowledge of the within-flock dynamics of Salmonella Enteritidis is required. Transmission of Salmonella Enteritidis has been quantified in pairs of layers, but the question is whether the dynamics in pairs is comparable to transmission in large groups, which are more representative for commercial layer flocks. The aim of this study was to compare results of transmission experiments between pairs and groups of laying hens. Experimental groups of either 2 or 200 hens were housed at similar densities, and 1 or 4 hens were inoculated with Salmonella Enteritidis, respectively. Excretion was monitored by regularly testing of fecal samples for the presence of Salmonella Enteritidis. Using mathematical modeling, the group experiments were simulated with transmission parameter estimates from the pairwise experiments. Transmission of the bacteria did not differ significantly between pairs or groups. This finding suggests that the transmission parameter estimates from small-scale experiments might be extrapolated to the field situation.